1. Field of the Invention
The present invention relates to a commutator and a method of manufacturing the same, and particularly to a commutator of a type wherein the inside of a main body thereof shaped substantially in the form of a cylinder and having a joint portion which is defined in a portion of an outer periphery of the main body and discontinues portions thereof adjacent to the joint portion, is charged with resin so as to mold a resin insulator made of the resin; and to a method of manufacturing the commutator.
2. Description of the Related Art
A commutator has a main body made of a metal and shaped in the form of a cylinder. In addition, the inside of the main body thereof is charged with resin so as to mold a resin insulator made of the resin. The thus-molded resin insulator is interposed about the axis of a rotor.
The commutator referred to above has heretofore been manufactured by a method of molding a metal plate in a predetermined form by pressing or the like, followed by rounding (a rounding process), joining both ends of the plate so as to form a cylindrical main body, and then charging the main body with resin so as to form a resin insulator made of the resin.
The method of molding the cylindrical main body from the metal plate (plate-like material) to fabricate the commutator has normally been used because the manufacturing process is easy and the material cost is reduced as compared with a method of molding a main body from a pipe-like material so as to fabricate a commutator.
However, the conventional commutator (main body) shaped in the form of a cylinder by rounding the plate-like material has a joint portion (joint surface) inevitably defined in a part of an outer peripheral wall of the commutator. Therefore, the conventional method has the problem that when the joint portion is charged with resin so as to mold a resin insulator, the resin flows out from the joint portion, thereby producing so-called burrs.
The resin (i.e., burrs), which flows out from the joint portion can cause an occurrence of sparks when windings for an armature coil are electrically connected to claw-shaped connecting portions (segments of a commutator) of the commutator by, for example, resistance welding. It is therefore necessary to establish a special working step for removing all burrs from the resin insulator after the resin insulator is molded, thereby causing poor workability and an increase in the manufacturing cost of the commutator.